This invention generally relates to computer disc drives and more particularly to a disc drive having a top cover that also performs the function of a voice coil motor pole.
The effort to make personal computers more compact has created demand to reduce the size of the disc drive used in personal computers. A major innovation in this direction has been the development of smaller, Winchester-type disc drives (hard disc drives) as replacements for floppy disc drives. Hard disc drives generally provide higher capacities and faster speeds of operation than floppy disc drives, factors which are of great importance for effective use of personal computers running advanced software packages. Many of these disc drives use voice coil motors for positioning a read/write transducer head over a selected track on the rotating hard disc.
The popularity of notebook computers and the advent of hand held computers has led to still another push to reduce the size of hard disk drives. Recently, efforts have been made to reduce the height of hard disc drives, so that the size of the housing for the computer could be minimized. However, further reduction of the physical size of a hard disc drive is constrained by the hard disc drive""s functional requirements. For example, the conventional voice coil motor requires at least two stationary magnets, a voice coil, a top pole, a bottom pole, and clearance space between each of these components. The size of these components may be minimized, but the components themselves may not be eliminated, unless the functionality of the components is provided by some other means.
A voice motor coil includes a magnetic circuit that creates a magnetic field operative to move an actuator assembly on which the read/write heads reside. Generally, a voice coil motor includes a top pole, a bottom pole, and a voice coil that moves between the poles. The top and bottom poles hold magnets, thereby creating a magnetic field therebetween. The poles function to provide magnetic paths, such that the magnets are in the magnetic paths with a cross flux to the coil. The voice coil motor moves when the voice coil is energized within the magnetic field. The actuator assembly moves when the voice coil is energized, thereby moving the read/write heads attached thereto.
A conventional disc drive 100 is depicted in FIG. 1. The disc drive 100 includes a base 120 to which various components of the disc drive 100 are mounted. A top cover 106, shown partially cut away, cooperates with the base 120 to form an internal, sealed environment for the disc drive in a conventional manner. A printed circuit board 102 is fastened to the underside of the baseplate 120. The internal components include a spindle motor 112 that rotates one or more discs 108 at a constant high speed. Information is written to and read from tracks on the discs 108 through the use of an actuator assembly 111, which rotates during a seek operation about a bearing shaft assembly 113 positioned adjacent the discs 108. The actuator assembly 111 includes a plurality of actuator arms 115 which extend towards the discs 108, with one or more flexures 116 extending from each of the actuator arms 115. Mounted at the distal end of each of the flexures 116 is a read/write head 118 (transducer) that includes an air bearing slider enabling the head 118 to fly in close proximity above the corresponding surface of the associated disc 108. During a seek operation, the track position of the head 118 is controlled through the use of a voice coil motor (VCM) 114.
A cross-sectional view of a conventional VCM is depicted in FIG. 2. Referring to FIGS. 1 and 2, the conventional VCM 114 includes a coil 126 attached to the actuator assembly 111. The conventional VCM also includes one or more bi-polar, stationary magnets 128 that establish a magnetic field in which the coil 126 is immersed. The controlled application of current to the coil 126 causes magnetic interaction between the stationary magnets 128 and the coil 126 so that the coil 126 moves in accordance with the well-known Lorentz relationship. The paths of the magnetic field are directed through a top pole 202 and a bottom pole 204 located above and below the voice coil 126. The top pole 202 and the bottom pole 204 are made of a magnetic permeable material, such as iron or steel. As the coil 126 moves in the magnetic field between the poles, the actuator assembly 111 pivots about the bearing shaft assembly 112, and the heads 118 are caused to move across the surfaces of the discs 108.
As discussed, the voice coil motor 110 includes an energizable coil 126 coupled to the actuator assembly 111 and a magnet assembly 200 coupled to the base 120 of the disc drive. In the disc drive depicted, the magnet assembly 200 includes a top pole plate and a bottom pole plate 202, 204. The poles 202, 204 are supported in spaced relation by at least two spacers 206 to form a gap 208 therebetween. The stationary magnets 128 are supported by the poles 202, 204 to form a permanent magnetic field in the gap 208. The poles 202, 204 support the bi-polar stationary magnets 128 to form two bi-directional flux paths 210, 212 for operation of the voice coil motor. The coil 126 extends into the gap 208 in alignment with the flux paths 210, 212 for generating a rotating force for operating the actuator assembly 111 proportional to current flowing through the coil 126.
There is a continual need for a smaller, simpler and more compact disc drive. One approach is to reduce the height of the disk drive. This may involve eliminating one or more of the parts of the voice coil motor (VCM) circuit. However, this approach still requires a complete magnetic circuit. Accordingly, there is a need for a low-height disc drive that reduces the overall height of the disc drive and yet is fully functional.
Against this backdrop the present invention has been developed. A low-height disc drive has a digital data storage disc rotatably mounted on a drive motor fastened to a base plate rotating the storage disc. The disc drive further includes an actuator assembly mounted to the base plate adjacent the storage disc, the actuator assembly including an actuator arm carrying a transducer for transferring data to and from the disc. The disc drive has a voice coil motor for rotating the actuator assembly to position the transducer with respect to the storage disc. The voice coil motor includes a voice coil fastened to the actuator arm, a stationary magnet attached to a bottom pole on the base plate in spaced, confrontational arrangement with a top pole defining a horizontal gap between the stationary magnet and the top pole through which the voice coil moves.
The hard disc drive of the present invention was specifically designed to be compact yet fully functional. The hard disc drive of the present invention has a magnetically-permeable top cover that functions as the top pole for the magnetic circuit of the voice coil motor (VCM). This functionality eliminates the need for a separate top pole for the VCM""s magnetic circuit. Because the need for the separate VCM pole has been eliminated, the hard disc drive can be manufactured such that it is more compact and less expensive than hard disc drives requiring a separate pole.
Alternatively, the top cover can be made of thin magnetically permeable material and folded in an accordion-like manner to provide the magnetic characteristics required to function as a top pole.